The present invention generally relates to apparatus for heating liquids and, more particularly, to providing dry fire protection for resistance type heating elements in electric water heaters.
Electric water heaters are used to heat and store a quantity of water in a storage tank for subsequent on-demand delivery to plumbing fixtures such as sinks, bathtubs and showers in both residences and commercial buildings. The electric water heaters typically utilize one or more electric resistance heating elements to supply heat to the tank-stored water under the control of a thermostat which monitors the temperature of the stored water.
An electric water heater is sold without water in it and is filled with water after it is moved to and installed in its intended operation location. The possibility exists that the water heater can be “dry fired”, i.e., have its electric resistance type heating element(s) energized before the storage tank is filled with water to immerse the heating element(s) projecting into its interior. When such dry firing occurs, each dry fired electric heating element typically burns out, resulting in a return of the unit to the manufacturer, or a service call by a repair technician to perform an on-site element replacement. The cost of either repair procedure can be quite substantial.
Various solutions have previously been proposed to prevent the firing of heating elements in electric water heaters unless the elements are immersed in water introduced into the storage tank of the water heater. Primarily, these proposed solutions have taken two forms, float switch-based protective systems and temperature sensor-based protective systems. However, neither of these previously proposed dry fire protection techniques has proven to be entirely satisfactory. For example, each tends to be fairly complex and undesirably expensive to incorporate into the overall water heater assembly. Additionally, these previously proposed systems have often proven to be unreliable, and tend to be undesirably invasive of the interior of the storage tank portion of the water heater.
In view of the foregoing, a need exists for improved dry fire protection system which overcomes certain difficulties with the prior art designs while providing better and more advantageous overall results.